1. Description of the Invention
This invention relates to a surface fastener to be used as a fastener of a disposable paper diaper, the surface fastener being improved in its attaching means so that the paper diaper is easy to handle.
2. Description of the Related Art
FIG. 10 of the accompanying drawings shows a paper diaper fastener which is disclosed in Japanese Utility Model Publication No. Hei 1-29230. In this known fastener, a plastic substrate tape 1xe2x80x2 has on its one surface an adhesive layer 7xe2x80x2 extending from the center to one end and a protective peel portion 8xe2x80x2 extending from the center to the other end. On the other surface, the plastic substrate tape 1xe2x80x2 has another protective peel portion 8xe2x80x2 extending from the center to one end and another adhesive layer 7xe2x80x2 extending from the center to the other end, which is a reverse arrangement to that on the one surface. The plastic substrate tape 1xe2x80x2 is attached in a folded form to a paper diaper Axe2x80x2 and, in use, the adhesive layer 7xe2x80x2 is peeled off the protective peel portion 8xe2x80x2 and is then adhered to a companion attaching section of the diaper Axe2x80x2.
Japanese Patent Laid-Open Publication No. Hei 2-5947 discloses a concept of using a surface fastener SF in a disposable diaper. As shown in FIG. 11, in the surface fastener, a thin strong flexible substrate plate 1 has on its front surface a multiplicity of resilient mushroom-shaped engaging elements 3xe2x80x3 each having a stem 3xe2x80x3b projecting upright from the front surface and a round head 3xe2x80x3a at the top of the stem 3xe2x80x3b. This surface fastener is fixed to an end of a flexible elongated rectangular polymer tab and is provided with a low-viscosity pressure-sensitive adhesive agent so that it is kept in a folded form; in use, the surface fastener is unfolded and is then fastened with a companion surface fastener.
According to the first-named conventional diaper fastener in a form of the plastic tape 1xe2x80x2, since the diaper Axe2x80x2 is fastened by the adhesive layer 7xe2x80x2, it is impossible to fasten the diaper Axe2x80x2 with adequate firmness. Further, the adhesive layer 7xe2x80x2 of the plastic tape 1xe2x80x2 tends to touch the infant""s skin which is very delicate when the diaper Axe2x80x2 is in use, so that the infant might suffer atopic dermatitis and other skin diseases.
According to the second-named conventional diaper fastener in a form of a surface fastener, since the engaging elements 3xe2x80x3 of the surface fastener SF have a very special shape, it is inevitable to use a very complicated processing means in manufacturing the surface fastener SF, and there is a danger that the pressure-sensitive adhesive agent on the polymer tab might touch the infant""s skin and cause atopic dermatitis or other skin diseases when the diaper is in use.
A first object of this invention is to provide a surface fastener which is suitable for a disposable paper diaper and in which either an adhesive layer or an adhesive double coated tape has such a form as not to contact an infant""s skin directly and which is easy to handle when the used paper diaper is to be cast off, at which time the used diaper is folded into a compact size and is wrapped in a simple manner.
A second object of the invention is to provide a surface fastener which is very simple to attach and handle with respect to a paper diaper.
A third object of the invention is to provide a surface fastener which is shaped into a form suitable for use in a paper diaper in view of relation between the adhesive strength of an adhesive layer and an adhesive double coated tape with respect to the surface fastener and the shape of engaging elements.
A fourth object of the invention is to provide a surface fastener which has a shape suitable for use in a paper diaper by specifying the surface fastener manufacturing means and shape.
A fifth object of the invention is to provide a surface fastener of which hook-shaped engaging elements are suitable for a paper diaper by specifying the hook-shaped engaging element manufacturing means.
A sixth object of the invention is to provide a paper diaper to which a surface fastener is attached in an optimal form and in which the surface fastener has such a shape that an adhesive layer and an adhesive double coated tape will not come into direct contact with an infant""s skin.
A seventh object of the invention is to provide a paper diaper in which a surface fastener can be attached in a simple manner and which can be handled simply when it is to be cast off after using.
According to a first aspect of the invention, there is provided a surface fastener comprising: a first substrate sheet having on its front surface a multiplicity of first engaging elements and on its rear surface a first adhesive layer; a second substrate sheet having on its front surface a multiplicity of second engaging elements engageable with the first engaging elements and on its rear surface a second adhesive layer; the first adhesive layer having an adhesive strength smaller than that of said second adhesive layer.
Preferably, the first adhesive layer is an adhesive double coated tape and has on its outer surface a backing sheet adhered thereto, while the second adhesive layer has on its outer surface a peel paper adhered thereto.
According to a second aspect of the invention, the backing sheet has on its outer surface another adhesive layer to an outer surface of which another peel paper is adhered.
According to a third aspect of the invention, the second engaging elements of the second substrate sheet on which the first-mentioned adhesive layer is disposed are loop-shaped engaging elements, and the first engaging elements of the first substrate sheet on which the adhesive double coated tape is disposed are hook-shaped engaging elements.
According to a fourth aspect of the invention, at least one of the first and second substrate sheets is knitted or woven, and the engaging elements of one of the first and second substrate sheets are hook-shaped engaging elements and/or loop-shaped engaging elements.
According to a fifth aspect of the invention, hook-shaped engaging elements are molded on the front surface of the first substrate sheet by injection molding.
According to a sixth aspect of the invention, there is provided a paper diaper using a plurality of surface fasteners, comprising a front covering portion and a hip covering portion having a plurality of attachment strips at its opposite sides, each surface fastener comprising: a first substrate sheet having on its front surface a multiplicity of first engaging elements; a second substrate sheet having on its front surface a multiplicity of second engaging elements engageable with the first engaging elements and on its rear surface an adhesive layer adhered to each of the opposite sides of the front covering portion; and an adhesive double coated tape adhered to a rear surface of the first substrate sheet with an adhesive strength smaller than that of the adhesive layer, the adhesive double coated tape being adhered to each of the attachment strips of the hip covering portion.
According to a seventh aspect of the invention, a backing sheet is adhered to an outer surface of the adhesive double coated tape and has on a surface opposite to the tape an additional adhesive layer of which outer surface is adhered to each of the attachment strips of the hip covering portion.
According to an eighth aspect of the invention, the second engaging elements of each second substrate sheet on which the first-mentioned adhesive layer is disposed are loop-shaped engaging elements, and the first engaging elements of each first substrate sheet on which the adhesive double coated tape is disposed are hook-shaped engaging elements.
According to a ninth aspect of the invention, the first or second substrate sheet is knitted or woven, and the engaging elements of the first or second substrate sheets are hook-shaped engaging elements and/or loop-shaped engaging elements.
According to a tenth aspect of the invention, the hook-shaped engaging elements are molded on the front surface of the first substrate sheet by injection molding.